From EPO493202B1 are known transparent panes provided with regular surface structures in which a structure impressed in the substrate is formed of pyramid-shaped recesses that are identical to each other and which are separated from each other by distances smaller than the biggest dimension of the recesses. The pyramids or truncated pyramids which are provided in them as a motif can be produced with a hexagonal or square base area but all have approximately plane side surfaces.
Combinations of embossing and of pyramids which protrude from their bottom have also been described. In particular, good light diffusion properties and a reduced visual detection of the presence of individual motifs which form the structure is obtained in this way due to a harmonious overall matt surface appearance.
Moreover, there is known, from WO03/046617A1, the manufacture and use of transparent plates (panes) provided with surface structures in the form of geometric relief which should improve the transmission of light and the light efficiency in particular for panes which are combined with solar cells (that is to say photoelectric cells or photovoltaic cells) and photovoltaic solar modules in solar collectors, flat plasma discharge lamps, image projection screens and projectors. The motifs of the geometric structure can in particular be concave with respect to the overall surface of the structured side of the pane, that is to say hot rolled into the initial substrate or formed in another appropriate way. In general, the motifs have a periodic shape, unlike that which is obtained by sandblasting or by etching methods. For technical production reasons (traversing speed, adhesion of rolled material on the rolls, etc.) it is not however possible to reproduce this periodicity with the desired accuracy. Moreover, undesirable periodic disturbances of the embossing operation can be added to it, for example due to dimensional deviations of the centering of the axes of the rolls when the rolling manufacturing method is used.
Because of this, on these structured surface panes, an optical phenomena is established by which the incident light is reflected differently by panes provided with the same surface motif and disposed or installed close to each other in the same plane or even within one and the same pane. In practice, depending on the assembly position, one part of the surface can reflect brilliantly and brightly whilst an immediately adjacent parallel part of surface has a matt appearance. Even through this effect is purely visual and aesthetic, it does not at all degrade the traversing of the light to the elements, detectors, etc., situated on the other side of the pane.
The cause of the variation of the impression of brightness according to the position on the pane is as follows.
Structures which are entirely regular in the ideal case have a characteristic reflection motif in which, for a given angle of incidence of light, the reflection takes place in specified directions and no reflection takes place in angular ranges which are adjacent to them. If, in a zone of the glass, because of the production tolerances mentioned above, the structures are formed on the surface of the glass in a (slightly) different manner, the characteristic direction of reflection of that zone of the glass is oriented in another direction (another angle). The consequence is that situations appear in which an observer is in the direction of reflection for one part of the glass but not in the direction of reflection of the other part of the glass. Thus, one zone of the glass has a bright appearance (reflecting) and the other as a dark appearance. In principle, this effect also takes place on glass with a smooth surface, but which is for example curved, which also has a bright reflection appearance only at certain places for given positions of the sun and of the observer.
However, it is possible to look for possibilities of giving these glasses a regular appearance of the light reflection in a particular mounting case.
The external appearance of these surfaces should not however be essentially different from the regular structures available at present, and in particular the panes should be able to be used beside one another.
U.S. Pat. No. 4,411,493 discloses a pane for building windows which must contribute to energy saving both in summer (air-conditioning) and in winter (heating). By a linear motif of parallel lines, there is obtained with this configuration a reflection or absorption behavior which strongly depends on the angle of incidence of the light.
Many cases are known of the use of surfaces that are chemically etched or treated by sandblasting in order to give them more or less irregular structures.
Fundamentally, there is known (see DE3805067A1 and DE4102984A1) the technique which consists in impressing random superficial structures on rolled surfaces using rolls on which random surface structures have been created. In all cases on continuously rolled substrates which are longer than one roll revolution, these structures are repeated periodically as a result of the regular rotation of the roll.